Novel mutation in TENM3 gene in an Iranian patient with colobomatous microphthalmia

This investigation revealed a homozygous c.5069-1G>C variation in TENM3 gene although has not been reported for its pathogenicity and can be considered as a novel mutation. The present finding can be used for genetic diagnosis and detection of carriers in the family and other patients with similar disease manifestations.

Genetic analysis of children with congenital ocular anomalies in three ecological regions of Nepal: a phase II of Nepal pediatric ocular diseases study

BACKGROUND

Genetic eye diseases constitute a large and heterogeneous group of childhood ocular morbidity. Individual diseases may cause multiple structural anomalies and developmental features. Nepal Pediatric Ocular Disease Study (NPODS) was a population-based epidemiological study conducted across three ecological regions of Nepal to determine the prevalence and etiology of childhood ocular morbidity and blindness. In Phase II of this study, genetic analysis was performed for children who were found to have congenital ocular anomalies.

METHOD

It was a cross sectional descriptive study. A total of 10,270 children across three different ecological regions in Nepal (Low lands, hills, and mountains) underwent ocular examinations in NPODS. Out of 374 (3.6%) of children with ocular abnormalities, 30 were thought to be congenital in nature. Targeted genetic analysis, including genotyping for genes specific to presenting phenotype, was performed for 25 children using serum samples.

RESULTS

Out of 25 children, 18 had meaningful genetic results. Analysis revealed one missense alteration G12411T of Zinc Finger Homeobox 4 (ZFHX4) gene in one participant among 10 with congenital ptosis and another missense variation T > C P. Y374 C of Signaling Receptor and Transporter Retinol 6 (STRA6) gene in one participant among 3 with microphthalmos.

CONCLUSION

The study is first of its kind from Nepal and mutant genes were unique to Nepalese Population. Further analysis of genetic factors is crucial to better understand genetic association with ocular diseases and conditions. This helps further in genetic counseling and probably gene therapy to prevent blindness from these conditions.

The heritability of ocular traits

Heritability is the proportion of phenotypic variation in a population that is attributable to genetic variation among individuals. Many ophthalmic disorders and biometric traits are known to have a genetic basis and consequently much work has been published in the literature estimating the heritability of various ocular parameters. We collated and summarized the findings of heritability studies conducted in the field of ophthalmology. We grouped the various studies broadly by phenotype as follows: refraction, primary open-angle glaucoma, age-related macular degeneration (AMD), cataract, diabetic retinopathy, and others. A total of 82 articles were retrieved from the literature relating to estimation of heritability for an ocular disease or biometric trait; of these, 37 papers were concerned with glaucoma, 28 with refraction, 4 with AMD, 5 with diabetic retinopathy, and 4 with cataract. The highest reported heritability for an ophthalmic trait is 0.99 for the phenotype ≥ 20 small hard drusen, indicating that observed variation in this parameter is largely governed by genetic factors. Over 60% of the studies employed a twin study design and a similar percentage utilized variance components methods and structural equation modeling (SEM) to derive their heritability values. Using modern SEM techniques, heritability estimates derived from twin subjects were generally higher than those from family data. Many of the estimates are in the moderate to high range, but to date the majority of genetic variants accounting for these findings have not been uncovered, hence much work remains to be undertaken to elucidate fully their molecular etiology.

Letter to the Editor: The Relative Contribution of the X Chromosome to Ocular Phenotypes

The X chromosome is unique, both in terms of functional expression and evolutionary history. Population frequencies for a minority of conditions, such as mental retardation, are directly related to the X chromosome. To explore these ideas, we investigated the general role of the X chromosome in ocular genetics through bioinformatic analysis of the distribution of eye-related genes in the human genome. The proportion of eye-disease loci located on the X chromosome compared to those eye diseases with an autosomal locus was calculated. The resultant figure (3.47) is lower than that calculated for mental retardation (9.74). A comparison between the number of X chromosome genes expressed in the eye compared to the number of autosomal genes expressed in the eye also did not reveal significant differences. Of all genes expressed in the eye, 2.9% are thought to be located on the X chromosome, fewer than found for the larger autosomes (which range from 10.1% to 3.6%). The eye's functional genetic components appear to be dispersed throughout the human genome, possibly to ensure survival in the event of significant cytogenetic derangement.

The Ocular Genetics Program: multidisciplinary care of patients with ocular genetic eye disease

BACKGROUND

Patients who suffer from ocular genetic diseases have special needs in terms of diagnosis and management of rare entities, low-vision needs, genetic counselling, and psychosocial adjustments that are usually not addressed by an ophthalmologist alone. The Ocular Genetics Program (OGP) at the Hospital for Sick Children, Toronto, was established in 1994 to provide comprehensive, multidisciplinary care of patients with inherited eye disorders. We now assess the benefits of such a program and of integrating research into the care of patients.

METHODS

We report our experience in developing a multidisciplinary ocular genetics program and the results of a pilot patient satisfaction survey that involved 61 patients.

RESULTS

The OGP multidisciplinary aspects are described. Of the 61 patients surveyed, 98% stated that they were satisfied with the OGP; 93%-96% of patients were content with "one day of appointments", "understanding of eye problem", and "coordination of ancillary tests such as visual fields test, electrophysiology, and others"; and for 70%-86% of respondents "waiting time to get an appointment", "information received on current research", and "primary health care provider adequately informed" were satisfactory.

INTERPRETATION

The OGP is a unique service in Canada, which strives to provide the comprehensive care needed by ocular genetic patients. High patient satisfaction is an indicator of the success of this approach. Long waiting times for appointments and application of laboratory research in clinical care remain challenging.

Autosomal dominant pattern dystrophy: identification of a novel splice site mutation in the peripherin/RDS gene

PURPOSE

To describe the clinical features of and identify the mutation responsible for an autosomal dominant pattern dystrophy occurring in a three-generation family.

METHODS

Five affected family members underwent clinical examination and additional testing including intravenous fluorescein angiography where indicated. Mutation screening of the peripherin/RDS gene was performed.

RESULTS

Visual acuity ranged from 20/20 to counting fingers. All patients who reported vision loss noted the onset after the age of 40 years. Predominantly perifoveal, discrete, retinal pigment epithelial changes were present in all patients. Two patients had extensive peripheral yellowish flecks, and one had an atrophic macular scar. Mutation screening of the complete peripherin/RDS coding sequence and exon/intron boundaries revealed a novel splice site mutation.

CONCLUSION

A three-generation family with an autosomal dominant pattern dystrophy arising from a previously unreported splice site mutation in the RDS gene is described.

The complexities of ocular genetics

The cliché 'a picture is worth a thousand words' is a testament to the power of the visual system in helping us deal with our physical environment. Rarely do perturbations to the visual system, even minor ones, go unnoticed. Major defects in eye development may occur in the absence of systemic problems which threaten health. Ocular anomalies offer a window into many developmental events which would otherwise be difficult to study.